Years of efforts ________ when they saw the pictures of the moon sent back to the earth by Changel．

1. A.
   showed off
2. B.
   took off
3. C.
   paid off
4. D.
   went off

Years of efforts        when they saw the pictures of the moon sent back to the earth by Chang’e-1.

A. paid off        B. took off        C. showed off      D. went off

Years of efforts     when they saw the pictures of the moon sent back to the earth by Chang’e-1.

A．paid off    B．took off    C．showed off      D．went off